Malignant Melanomas arising in the choroid and ciliary body constitute the most frequent primary intraocular malignancy. Blindness usually results, and the long-term mortality from metastatic disease approaches 50 percent. However; uveal melanomas also offer a unique opportunity for studying a neoplastic system, since tumors of all size have essentially equal opportunity for hematogenous dissemilation as a result of the extreme vascularity of the uvea, and since the tough scleral coat of the eye prevents direct extraocular extension in all but the most exceptional cases. Thus, uveal melanoma is both a clinically significant entity and a nearly ideal model system in which to study the histopathologic criteria of malignancy. Our objective is to develop an objective and reproducible method for determining the malignant potential of uveal melanomas from histopathologic examination. In order to achieve this objective, we will measure the cytologic features from the microslides of several hundred uveal melanomas selected from the Registry of Ophthalmic Pathology (Armed Forces Institute of Pathology). After comparing these measurements with the clinical course of the patients from whom the tumors were removed, we will select those cytologic features that are useful for predicting death from metastasis. With this information we will develop objective criteria for estimating the malignant potential of newly-diagnosed cases of uveal melanoma. Ultimately, concepts derived from the study of this relatively controlled neoplastic system will be applied to other neoplasms in an attempt to predict their malignant potential.